For the electrostatic coating with direct charging of an electrically conductive coating material of different colors, it has been customary for some time to use an intermediate container, which is supplied by the atomizer. The required potential separation between the color changer can be provided between the one grounded and the atomizer running on high voltage. This container can also be filled by the color changer, if the high voltage at the atomizer has been switched off or the feed line to the atomizer has been emptied prior to the supply flow crossing the insulation gap of the supply line. The insulation gap must be recreated between the container and the color changer, for example by draining the supply line of the container (EP 0 292 778 A2; U.S. Pat. No. 4,932,589; DE 199 37 426 A1; EP 1 314 483 A2; and EP 1 362 642 A1). It is especially advisable to design this intermediate container as a metering cylinder, depending on the range of production colors, precisely for the metering of the atomizer and, for this purpose, it would be configured to include an electrical motor driven by a threaded spindle and by a small piston rod driven piston.
If only one single intermediate container is to be used, as previously done after its discharge, the coating process had to be interrupted until the container had been recharged by the color changer. For the above mentioned state of the art, and to prevent this disadvantage, it has been customary and common to connect two alternating metering cylinders in parallel (A/B-operation) between the color changer and the atomizer, so that during the supply of the atomizer from the other container, the idle metering cylinder may be recharged. Aside from the two separate metering cylinders and their expense, this well known configuration has however the disadvantage of requiring more space, which in some cases may be undesirable, as for example in limited interior spaces of painting machines, such as in the front arm of a robot. Particularly undesirable is a higher space requirement of the additional metering cylinder, if it is to be self-installed into the atomizer, as this tends to make it to unwieldy for the accessibility of work areas or interior areas, or into the wrist of a painting robot as described in the concurrent German Patent Application 10 2004 058 054.